In a mobile terminal communication system, a baseband signal is modulated into a radio frequency signal, which is transmitted by an antenna into the air after being amplified by a power amplifier. The power amplifier is a main power-consuming module of a mobile terminal, and in an operation process, the power amplifier converts, under the control of a transistor, direct current power supplied by a power source to the power amplifier into alternating current power on a load. Generally, the efficiency η of the power amplifier means a ratio of the alternating current power Psc to the direct current power PE supplied by the power source, and is usually represented by a percentage, that is, η=Psc/PE×100%.
Because the transistor itself needs to consume some power, and various circuit elements (such as resistors and transformers) also need to consume some power, the direct current power supplied by the power source to the power amplifier cannot be fully converted into the alternating current power on the load. In a wideband code division multiple access (Wideband Code Division Multiple Access, WCDMA for short) system, the efficiency η of the power amplifier varies with a change of the alternating current power, that is, the transmit power; when the transmit power reaches the highest level of the system, the efficiency η of the power amplifier is also the highest and may be up to 40%; and when the transmit power is small, the efficiency η of the power amplifier is less than 10%. Because the power source of the power amplifier is generally a battery, too low efficiency not only causes an unnecessary waste of electricity energy of the battery, but also greatly shortens the life of the battery, thus reducing the operation time of the mobile terminal.
In order to decrease the power consumption generated by the power amplifier and raise the efficiency η of the power amplifier, the prior art provides a technical solution of achieving the objective of decreasing the power consumption of the system by changing the gain mode of the power amplifier. The supply voltage of the power amplifier is one of factors affecting the gain of the power amplifier, and is also a major factor affecting the power consumption of the power amplifier. Generally, the higher the supply voltage, the higher the gain. Therefore, in the technical solution of the prior art, the operation modes of the power amplifier are classified into three levels: high gain, medium gain, and low gain. The three gain modes sequentially correspond to three different supply voltages in descending order. The level at which the supply voltage of the power amplifier is, that is, the level at which the gain mode is, is determined according to the actual gain value of the power amplifier in the operation process.
When implementing the present invention, the inventor finds that the power amplifier using the foregoing technical solution may also achieve, to a certain degree, the objective of decreasing power consumption, but this classification method is too rough, so that the effect of decreasing the power consumption of the power amplifier is not very obvious.